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Effects of vegetation buffer strips on concentrated flow hydraulics and gully bed erosion based on in situ scouring experiments

Dong, Yifan, Xiong, Donghong, Su, Zheng'an, Yang, Dan, Zheng, Xueyong, Shi, Liangtao, Poesen, Jean
Land degradation & development 2018 v.29 no.6 pp. 1672-1682
conservation buffers, flow resistance, runoff, sediments, soil, vegetation
Vegetation on gully beds could intercept runoff, reduce incision of gully bed, and trap sediment from upstream area. The aim of this study is to evaluate the influences of vegetation buffer strips on concentrated flow hydraulics and gully bed erosion downstream of gully headcuts. Five gully head plots containing different buffer strip widths with similar vegetation density were constructed for in situ scouring experiments. Each plot received 11 tests with 2 discharges (i.e., 7 tests simulating 83.3 L min⁻¹ and 4 tests simulating 166.7 L min⁻¹). Buffer strips clearly decrease flow hydraulics (about 56–70%) and increase flow resistance (1.2 to 1.5 times) according to the selected hydraulic parameters. After 11 tests, total net erosion volume (NEV) and average sediment concentration from each gully bed showed an exponential decreasing relationship with increasing widths of buffer strips. All the selected hydraulic parameters showed a strong correlation with total NEV from the bare soil sections (0.43 < R² < .61 with significance level reaching .01), whereas the relationship was very weak in the buffer strips. The gross deposition volume in buffer strips showed a linear correlation with upstream NEV (NEVᵤ) and flow velocity (R² = .91, p < .001). Split flow effects expressed by braid index increased with increasing widths of buffer strips and scouring times. Both bare and vegetated sections suffered from erosion clearly, but the average NEV from buffer strips was about 30.2% of bare soil sections. This indicated the buffer strip effects on reducing erosion were more significant than trapping sediments were in this study.